What is lost-wax bell casting?
The lost-wax bell casting process is a method of bell casting which a molten metal (usually bronze, brass, gold or silver) is poured into a mold created by a wax model of the original bell sculpture. The lost-wax casting process was widespread in Europe until the 18th century, when the piece-moulding process became a more prominent method of bell casting.
The making of a lost-wax casting bell starts with the inside and the outside drawing of the original bell shape on a metallic or a wooden board, called a strickle board. These two drawings define the bell profile while the musical characteristics of a bell, such as note accuracy, sound, depth, and tonal richness are determined by its shape.
The strickle board, once mounted on a pivot, is used to build the bell mold, which is composed of three well defined superimposed parts: the core, the false bell and the cope.
The core, also called the inside mold of the bell, is made of sand and bricks covered with clay.
The False Bell
The false bell, made with sand, has the exact same dimensions, diameter, height, thickness and profile as the original bell. It is coated with a thin layer of soft wax, then decorated with design garlands, ornamentations and inscriptions. All letters and decorations are made of wax and are raised from the surface of the false bell.
The cope, which is the outside part of the mold, is built up by the foundry craftsmen on the false bell and is made of several coats of clay reinforced by hemp. When the parts are dry, the inside of the core is heated. The wax melts and then drains out from the mold, creating an indentation (or hollow relief) in the cope for the decorations and inscriptions.
The cope is secured in a metallic cover called the molding flask. Using overhead rigging, rope and tackle, the cope is raised and the false bell is broken away and removed. The cope is then placed back on top of the core, leaving an empty space where the false bell was created. The molten metal will then be poured into the empty space.
The bronze, an alloy of approximately 78% copper and 22% tin, is melted and checked after five hours of heating. When it reaches 2,200 degrees Fahrenheit, the molten metal is poured into the mold through a channel where the gas flames also escape.
The Lost-wax Process Final Product
A few days later, the burnt mold is lifted up and broken to reveal a black and gray bell. After a careful sandblasting of the larger remaining particles of the mold and a fine polish, the final lustrous bronze bell emerges.